Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video encoding/decoding. In some examples, an apparatus for video decoding includes receiving circuitry and processing circuitry. In some embodiments, the processing circuitry decodes prediction information of a current block from a coded video bitstream. The prediction information is indicative of an intra prediction mode. Then, the processing circuitry determines whether the current block meets a block size condition that limits an application of a position dependent intra prediction combination (PDPC) in reconstructions of the current block based on sizes of the current block. When the block size condition is met, the processing circuitry excludes the application of the PDPC in a reconstruction of at least one sample of the current block based on the intra prediction mode.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/713,391, “IMPROVEMENT FOR POSITIONDEPENDENT INTRA PREDICTION COMBINATION (PDPC)” filed on Aug. 1, 2018,which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEM/VVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

FIG. 2 shows a schematic (201) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions over time.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions that are statistically less likely tooccur in video content than certain other directions. As the goal ofvideo compression is the reduction of redundancy, those less likelydirections will, in a well working video coding technology, berepresented by a larger number of bits than more likely directions.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus for video decodingincludes receiving circuitry and processing circuitry. In someembodiments, the processing circuitry decodes prediction information ofa current block from a coded video bitstream. The prediction informationis indicative of an intra prediction mode. Then, the processingcircuitry determines whether the current block meets a block sizecondition that limits an application of a position dependent intraprediction combination (PDPC) in reconstructions of the current blockbased on sizes of the current block. When the block size condition ismet, the processing circuitry excludes the application of the PDPC in areconstruction of at least one sample of the current block based on theintra prediction mode.

According to an aspect of the disclosure, the block size conditionlimits the application of the PDPC in the reconstructions of the currentblock when the application of the PDPC in the reconstructions of thecurrent block uses additional reference samples other than referencesamples used in angular based intra prediction according to the intraprediction mode.

In an embodiment, the processing circuitry determines whether one of awidth and a height of the current block is equal to two, and disablesthe application of the PDPC in the reconstruction of the current blockwhen one of the weight and the height of the current block is equal totwo.

In another embodiment, the processing circuitry determines whether thecurrent block is larger than a size threshold and disables theapplication of the PDPC in the reconstruction of the current block whenthe current block is larger than the size threshold.

In another embodiment, the processing circuitry determines whether aratio of two sides of the current block meets a narrow shape conditionand disables the application of the PDPC in the reconstruction of thecurrent block when the ratio meets the narrow shape condition.

In another embodiment, when the block size condition is met, theprocessing circuitry selects a subset of samples in the current blockfor the application of the PDPC, reconstructs the subset of samples withthe application of the PDPC, and reconstructs at least one other samplein the current block without the application of the PDPC. For example,the processing circuitry selects one or more left columns in the currentblock for the application of the PDPC when the current block has morecolumns than rows and the intra prediction mode is a diagonal mode. Inanother example, the processing circuitry selects one or more top rowsin the current block for the application of the PDPC when the currentblock has more rows than columns and the intra prediction mode is adiagonal mode.

In some embodiments, the processing circuitry increases a descendingspeed of a weight for weighting reference samples, the weight descendingalong a side of the current block according to the descending speed. Insome examples, the processing circuitry reduces an initial value of aweight for weighting reference samples, the weight descending along aside of the current block from the initial value. In some examples, theprocessing circuitry sets a first descending speed for weighting in thePDPC for a chroma component to be larger than a second descending speedfor weighting in the PDPC for a luma component.

In some embodiments, the processing circuitry disables the applicationof the PDPC in the reconstruction of chroma samples. In an example, theprocessing circuitry disables the application of the PDPC in thereconstruction of chroma samples when the intra prediction mode is onein a predefined set of intra prediction modes.

In some embodiments, the processing circuitry determines initial valuesfor weights that descend along sides of the current block based on atleast one of a color index, sizes of the current block and the intraprediction mode.

In some embodiments, the processing circuitry determines whether areference sample in the application of the PDPC is out of a predefinedrange and sets a weight for the reference sample to be zero when thereference sample is out of the predefined range.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the method forvideo decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of an exemplary subset of intraprediction modes.

FIG. 2 is an illustration of exemplary intra prediction directions.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 6 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 7 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 8 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 9 shows an illustration of exemplary intra prediction directionsand the intra prediction modes used in HEVC.

FIGS. 10A-10B show weights for prediction samples according to someembodiments.

FIG. 11 shows a flow chart outlining a process example 1100 according tosome embodiments of the disclosure.

FIG. 12 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the FIG. 3 example, the first pair of terminal devices (310) and(320) performs unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (330) and (340)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (330) and (340) via the network (350). Eachterminal device of the terminal devices (330) and (340) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (330) and (340), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 3 example, the terminal devices (310), (320), (330) and(340) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (350) represents any number ofnetworks that convey coded video data among the terminal devices (310),(320), (330) and (340), including for example wireline (wired) and/orwireless communication networks. The communication network (350) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(350) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (413), that caninclude a video source (401), for example a digital camera, creating forexample a stream of video pictures (402) that are uncompressed. In anexample, the stream of video pictures (402) includes samples that aretaken by the digital camera. The stream of video pictures (402),depicted as a bold line to emphasize a high data volume when compared toencoded video data (404) (or coded video bitstreams), can be processedby an electronic device (420) that includes a video encoder (403)coupled to the video source (401). The video encoder (403) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (404) (or encoded video bitstream (404)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (402), can be stored on a streamingserver (405) for future use. One or more streaming client subsystems,such as client subsystems (406) and (408) in FIG. 4 can access thestreaming server (405) to retrieve copies (407) and (409) of the encodedvideo data (404). A client subsystem (406) can include a video decoder(410), for example, in an electronic device (430). The video decoder(410) decodes the incoming copy (407) of the encoded video data andcreates an outgoing stream of video pictures (411) that can be renderedon a display (412) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (404),(407), and (409) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anembodiment of the present disclosure. The video decoder (510) can beincluded in an electronic device (530). The electronic device (530) caninclude a receiver (531) (e.g., receiving circuitry). The video decoder(510) can be used in the place of the video decoder (410) in the FIG. 4example.

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (501), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (531) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (531) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (515) may be coupled inbetween the receiver (531) and an entropy decoder/parser (520) (“parser(520)” henceforth). In certain applications, the buffer memory (515) ispart of the video decoder (510). In others, it can be outside of thevideo decoder (510) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (510), forexample to combat network jitter, and in addition another buffer memory(515) inside the video decoder (510), for example to handle playouttiming. When the receiver (531) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (515) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (515) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such as arender device (512) (e.g., a display screen) that is not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as was shown in FIG. 5. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (520) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (520) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (520). The flow of such subgroup control information between theparser (520) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values, thatcan be input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (558). The currentpicture buffer (558) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(555), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (552) has generated to the outputsample information as provided by the scaler/inverse transform unit(551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (521) pertaining to the block, these samples can beadded by the aggregator (555) to the output of the scaler/inversetransform unit (551) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (557) from where themotion compensation prediction unit (553) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (553) in the form of symbols (521) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (557) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (556) can be a sample stream that canbe output to the render device (512) as well as stored in the referencepicture memory (557) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (520)), the current picture buffer (558) can becomea part of the reference picture memory (557), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (531) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (510) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anembodiment of the present disclosure. The video encoder (603) isincluded in an electronic device (620). The electronic device (620)includes a transmitter (640) (e.g., transmitting circuitry). The videoencoder (603) can be used in the place of the video encoder (403) in theFIG. 4 example.

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the FIG. 6example) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) is a part ofthe electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (601) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (601) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (603) may code andcompress the pictures of the source video sequence into a coded videosequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (650). In some embodiments, the controller(650) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (650) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (650) can be configured to have other suitablefunctions that pertain to the video encoder (603) optimized for acertain system design.

In some embodiments, the video encoder (603) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (630) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (633)embedded in the video encoder (603). The decoder (633) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (634). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (634) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5. Brieflyreferring also to FIG. 5, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (630) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (632) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (640) may transmit additional datawith the encoded video. The source coder (630) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherembodiment of the disclosure. The video encoder (703) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (703) is used in theplace of the video encoder (403) in the FIG. 4 example.

In an HEVC example, the video encoder (703) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (703) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (703) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 7 example, the video encoder (703) includes the interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in FIG. 7.

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (722) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (721) is configured to determine general controldata and control other components of the video encoder (703) based onthe general control data. In an example, the general controller (721)determines the mode of the block, and provides a control signal to theswitch (726) based on the mode. For example, when the mode is the intramode, the general controller (721) controls the switch (726) to selectthe intra mode result for use by the residue calculator (723), andcontrols the entropy encoder (725) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(721) controls the switch (726) to select the inter prediction resultfor use by the residue calculator (723), and controls the entropyencoder (725) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (723) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (722) or the inter encoder (730). Theresidue encoder (724) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (724) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (703) also includes a residuedecoder (728). The residue decoder (728) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (722) and theinter encoder (730). For example, the inter encoder (730) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (722) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (725) is configured to format the bitstream toinclude the encoded block. The entropy encoder (725) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (725) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 8 shows a diagram of a video decoder (810) according to anotherembodiment of the disclosure. The video decoder (810) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (810) is used in the place of the videodecoder (410) in the FIG. 4 example.

In the FIG. 8 example, the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residue decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in FIG. 8.

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (872) or the inter decoder (880), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (880); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (872). The residual information can be subject to inversequantization and is provided to the residue decoder (873).

The inter decoder (880) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (872) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (873) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (873) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (871) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (874) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (873) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In an embodiment, the video encoders (403), (603),and (703), and the video decoders (410), (510), and (810) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Aspects of the disclosure provide improvement techniques for positiondependent intra prediction combination (PDPC). The PDPC is used in theintra prediction, and invokes a combination of the un-filtered boundaryreference samples and HEVC style intra prediction with filtered boundaryreference samples. The HEVC style intra prediction with filteredboundary reference samples is also referred to as angular based intraprediction.

FIG. 9 shows an illustration of exemplary intra prediction directionsand the intra prediction modes used in HEVC. In HEVC, there are total 35intra prediction modes (mode 0 to mode 34), among which mode 10 ishorizontal mode, mode 26 is vertical mode, and mode 2, mode 18 and mode34 are diagonal modes. In some examples, the intra prediction modes aresignaled by three most probable modes (MPMs) and 32 remaining modes.

As shown in FIG. 2, in some examples (e.g., VVC), there are total 67intra prediction modes (mode 0 to mode 66), where mode 18 is horizontalmode, mode 50 is vertical mode, and mode 2, mode 34 and mode 66 arediagonal modes.

In some examples, the HEVC style intra prediction is based on filteredreference samples. For example, when the intra prediction mode is notany of the DC mode and the planar mode, a filter is applied to theboundary reference samples, and the filtered reference samples are usedto predict values in the current block based on the intra predictionmode.

According to some embodiments, PDPC combines the un-filtered boundaryreference samples and HEVC style intra prediction with filtered boundaryreference samples. In an example, according to PDPC, when the intraprediction mode is planar mode (e.g., mode 0), vertical mode (e.g., mode50 in the case of 67 intra prediction modes), horizontal mode (e.g.,mode 18 in the case of 67 intra prediction modes), each predictionsample pred′[x][y] located at (x, y) is calculated according to Eq. 1:

pred′[x][y]=(wL×R(−1,y)+wT×R(x,−1)+wTL×R(−1,−1)+(64−wL−wT−wTL)×pred[x][y]+32)>>6  (Eq.1)

where R(x,−1), R(−1,y) represent the unfiltered reference sampleslocated at top and left of current sample (x, y), respectively, R(−1,−1)represents the unfiltered reference sample located at the top-leftcorner of the current block, and wT, wL, and wTL denote weights. Theweights are calculated by Eq. 2-Eq. 5, width denotes the width of thecurrent block, and height denotes the height of the current block:

wT=32>>((y<<1)>>shift)  (Eq. 2)

wL=32>>((x<<1)>>shift)  (Eq. 3)

wTL=−(wL>>4)−(wT>>4)  (Eq. 4)

shift=(log 2(width)+log 2(height)+2)>>2  (Eq. 5)

FIG. 10A shows weights for prediction sample at (0, 0). In the FIG. 10Aexample, the current block is a 4×4 block, width is 4, height is also 4,thus shift is 1. Then, wT is 32, wL is 32, and wTL is −4.

FIG. 10B shows weights for prediction sample at (1,0). In the FIG. 10Bexample, the current block is a 4×4 block, width is 4, height is also 4,thus shift is 1. Then, wT is 32, wL is 16, and wTL is −3.

More generally, in some examples, inputs to the PDPC process includes:

the intra prediction mode that is represented by predModeIntra;

the width of the current block that is represented nTbW;

the height of the current block that is represented by nTbH;

the width of the reference samples that is represented by refW;

the height of the reference samples that is represented by refH;

the predicted samples by HEVC style intra prediction that arerepresented by predSamples[x][y], with x=0 . . . nTbW−1 and y=0 . . .nTbH−1;

the unfiltered reference (also referred to as neighboring) samplesp[x][y], with x=−1, y=−1 . . . refH−1 and x=0 . . . refW−1, y=−1; and

the colour component of the current block that is represented by cIdx.

Further, the outputs of the PDPC process are the modified predictedsamples predSamples′[x][y] with x=0 . . . nTbW−1, y=0 . . . nTbH−1.

Then, a scaling factor nScale (shift in the above description) iscalculated by Eq. 6 which is similar to Eq. 5:

((Log 2(nTbW)+Log 2(nTbH)−2)>>2)  (Eq. 6)

Further, a reference sample array mainRef[x] with x=0 . . . refW isdefined as the array of unfiltered reference samples above the currentblock and another reference sample array sideRef[y] with y=0 . . . refHis defined as the array of unfiltered reference samples to the left ofthe current block, and can be derived from unfiltered reference samplesaccording to Eq. 7 and Eq. 8:

mainRef[x]=p[x][−1]  (Eq. 7)

sideRef[y]=p[−1][y]  (Eq. 8)

For each location (x,y) in the current block, the PDPC calculation usesa reference sample at the top that is denoted as refT[x][y], a referencesample at the left that is denoted as refL[x][y], and a reference sampleat the corner p[−1,−1]. In some examples, the modified predicted sampleis calculated by Eq. 9 in some examples, and the result is suitablyclipped according to the cIdx variable that is indicative of the colorcomponent.

predSamples′[x][y]=(wL×refL(x,y)+wT×refT(x,y)+wTL×p(−1,−1)−(64−wL−wT+wTL)×predSamples[x][y]+32)>>6  (Eq.9)

The reference samples refT[x][y], refL[x][y], and the weights wL, wT andwTL can be determined based on the intra prediction mode predModelIntra.

In an example, when the intra prediction mode predModeIntra is equal toINTRA_PLANAR (e.g., 0, planar mode, mode 0), INTRA_DC (e.g., 1, DC mode,mode 1), INTRA_ANGULAR18 (e.g., 18, horizontal mode, mode 18 in the caseof 67 intra prediction modes), or INTRA_ANGULAR50 (e.g., 50, verticalmode, mode 50 in the case of 67 intra prediction modes), referencesamples refT[x][y], refL[x][y], and the weights wL, wT and wTL can bedetermined according to Eq. 10-Eq. 14:

refL[x][y]=p[−1][y]  (Eq. 10)

refT[x][y]=p[x][−1]  (Eq. 11)

wT[y]=32 >>((y<<1)>>nScale)  (Eq. 12)

wL[x]=32 >>((x<<1)>>nScale)  (Eq. 13)

wTL[x][y]=(predModeIntra==INTRA_DC)?((wL[x]>>4)+(wT[y]>>4)):0  (Eq. 14)

In another example, when the intra prediction mode predModeIntra isequal to INTRA_ANGULAR2 (e.g., 2, mode 2 in the case of 67 intraprediction mode) or INTRA_ANGULAR66 (e.g., 66, mode 66 in the case of 66intra prediction mode), reference samples refT[x][y], refL[x][y], andthe weights wL, wT and wTL can be determined according to Eq. 15-Eq. 19:

refL[x][y]=p[−1][x+y+1]  (Eq. 15)

refT[x][y]=p[x+y+1][−1]  (Eq. 16)

wT[y]=32>>((y<<1)>>nScale)  (Eq. 17)

wL[x]=32>>((x<<1)>>nScale)  (Eq. 18)

wTL[x][y]=0  (Eq. 19)

In another example, when the intra prediction mode predModeIntra is lessthan or equal to INTRA_ANGULAR10 (e.g., 10, mode 10 in the case of 67intra prediction mode), for location (x, y), variables dXPos[y],dXFrac[y], dXInt[y] and dX[y] are derived based on a variable invAnglethat is a function of the intra prediction mode predModeIntra. In anexample, the invAngle can be determined based on a look-up table thatstores a corresponding invAngle value to each intra prediction mode, andthen the reference samples refT[x][y], refL[x][y], and the weights wL,wT and wTL are determined based on the variables dXPos[y], dXFrac[y],dXInt[y] and dX[y].

For example, the variables dXPos[y], dXFrac[y], dXInt[y] and dX[y] aredetermined according to Eq. 20-23:

dXPos[y]=((y+1)×invAngle+2)>>2  (Eq. 20)

dXFrac[y]=dXPos[y]& 63  (Eq. 21)

dXInt[y]=dXPos[y]>>6  (Eq. 22)

dX[y]=x+dXInt[y]  (Eq. 23)

Then, the reference samples refT[x][y], refL[x][y], and the weights wL,wT and wTL are determined according to Eq. 24-Eq. 28.

refL[x][y]=0  (Eq. 24)

refT[x][y]=(dX[y]<refW−1)?((64−dXFrac[y])×mainRef[dX[y]]+dXFrac[y]×mainRef[dX[y]+1]+32)>>6:0  (Eq.25)

wT[y]=(dX[y]<refW−1)?32 >>((y<<1)>>nScale):0  (Eq. 26)

wL[x]=0  (Eq. 27)

wTL[x][y]=0  (Eq. 28)

In another example, when the intra prediction mode predModeIntra isgreater than or equal to INTRA_ANGULAR58 (e.g., 58, mode 58 in the caseof 67 intra prediction modes), variables dYPos[x], dYFrac[x], dYInt[x]and dY[x] are derived based on a variable invAngle that is a function ofthe intra prediction mode predModeIntra. In an example, the invAngle canbe determined based on a look-up table that stores a correspondinginvAngle value to each intra prediction mode, and then the referencesamples refT[x][y], refL[x][y], and the weights wL, wT and wTL aredetermined based on the variables dYPos[x], dYFrac[x], dYInt[x] anddY[x].

For example, the variables dYPos[x], dYFrac[x], dYInt[x] and dY[x] aredetermined according to Eq. 29-33:

dYPos[x]=((x+1)×invAngle+2)>>2  (Eq. 29)

dYFrac[x]=dYPos[x]&63  (Eq. 30)

dYInt[x]=dYPos[x]>>6  (Eq. 31)

dY[x]=x+dYInt[x]  (Eq. 32)

Then, the reference samples refL[x][y], refL[x][y], and the weights wL,wT and wTL are determined according to Eq. 33-Eq. 37.

refL[x][y]=(dY[x]<refH−1)?((64−dYFrac[x])×sideRef[dY[x]]+dYFrac[x]×sideRef[dY[x]+1]+32)>>6:0  (Eq.33)

refT[x][y]=0  (Eq. 34)

wT[y]=0  (Eq. 35)

wL[x]=(dY[x]<refH−1)?32>>((x<<1)>>nScale):0  (Eq. 36)

wTL[x][y]=0  (Eq. 37)

In some examples, when the variable predModeIntra is between 11-57 andis not one of 18 and 50, then the refL[x][y], refT[x][y], wT[y], wL[y]and wTL[x][y] are all set equal to 0.

It is noted that some PDPC processes include non-integer (e.g., floatingpoint) operations that increase computation complexity. In someembodiments, the PDPC process includes relatively simple computationsfor the planar mode (mode 0), the DC mode (mode 1), the vertical mode(e.g., mode 50 in the case of 67 intra prediction modes), the horizontalmode (e.g., mode 18 in the case of 67 intra prediction modes), and thediagonal modes (e.g., mode 2, mode 66, and mode 34 in the case of 67intra prediction modes), and the PDPC process includes relativelycomplex computations for the other modes.

According to some aspects of the disclosure, in certain situations, thePDPC process uses more reference samples than regular angular intraprediction process, and causes more burden of delay, complexity indecoding. The tradeoff between complexity and coding efficiency in thePDPC can be improved with some limitations for applying the PDPC. Thelimitations are set to avoid potential scenarios of PDPC that uses morereference samples than regular intra prediction process or avoidpotential scenarios of PDPC that the extra computation load by the PDPCdoes not justify the benefit.

The proposed methods may be used separately or combined in any order. Inthis document, current block can refer to chroma components of currentblock, or luma component of block, or both luma and chroma components ofcurrent block.

When padding an array/buffer of N reference samples, it means thereference sample values are either filled by the neighboringreconstructed samples located at the associated position of referencesamples, or copied from reference samples that have already been filled,or derived from reference samples that have already been filled using apre-defined function (e.g., linear extrapolation).

According to an aspect of the disclosure, PDPC is applied to certainblock sizes instead of all block sizes. In some embodiments, the blocksize of a current block is checked to determine whether to apply thePDPC process.

In an embodiment, PDPC is not applied to 2×N or N×2 blocks, where N canbe 2, 4, 8, 16, 32, 64, or 128.

In another embodiment, PDPC is not applied to 2×N or N×2 blocks, where Nis equal to or larger than 32.

In another embodiment, PDPC is not applied to M×N blocks, where M or Nis equal to or larger than 32.

In another embodiment, PDPC is not applied to M×N blocks, where both Mand N is equal to or larger than 32.

In another embodiment, PDPC is not applied to narrow blocks. Forexample, a narrow block is defined based on a size ratio of a large sideof the block to a small side of the block. For example, the size ratiois calculated between max(width, height) and min(width, height) ofcurrent block. When the size ration is equal to or larger than athreshold, such as thres_ratio, the current block is considered as anarrow block The threshold_thres ratio can be 4, 8, 16, 32, or 64 insome examples. For example, 4×16 or 16×4 blocks are referred to asnarrow blocks when the threshold thres_ratio is set to 4. The thresholdthres_ratio may also be signaled in bitstream such as in sequenceparameter set (SPS), picture parameter set (PPS), or slice header.

In another embodiment, PDPC is not applied to large blocks. In anexample, when the number of pixels in the current block is equal to orlarger than a pixel threshold, the current block is considered as alarge block, and PDPC is not applied to the large block. The pixelthreshold can be any suitable number, such as 32, 64, 128, 256, 512,1024, or 2048.

According to another aspect of the disclosure, PDPC is applied to aportion of the current block with a certainty that the unfilteredreference samples are available for the portion of the current block.The portion of the current block can be certain columns or certain rowsof current block.

In some embodiments, the portion of the current block where PDPC isapplied is determined based on a minimum value of the width and heightof the current block. In an example, the width of the current block isM, and the height of the current block is N. When M is larger than N,the PDPC is applied to the first left N columns of the current block;when M is smaller than N, the PDPC is applied to the first top M rows ofthe current block. For example, the current block has a size of 2×32(width by height), PDPC is then applied to the 2 top rows of currentblock. For another example, the current block has a size of 32×2 (widthby height), PDPC is then applied to 2 left columns of current block.

In an example, for certain intra prediction mode, the PDPC is applied toa portion of the current block. For example, when the intra predictionmode is mode 2 or mode 66 in the case of the 67 intra prediction modes,the PDPC is applied to a portion of the current block that is determinedbased on the minimum value of the width and the height of the currentblock.

In another example, the PDPC is applied to the first N columns or thefirst N rows in the current block. The value of N can be any suitablenumber, such as 1, 2, 3, 4, 5, 6, . . . , 8.

In another embodiment, the descending speeds of weights (from top row tobottom row and from left column to the right column) for the unfilteredreference samples in the PDPC are set up differently for the chromacomponent from the luma component to cause the chroma component to havehigher descending speed weight than the luma component. It is noted thatwhen a weight is descended to zero, then there is no need to access thecorresponding reference sample. In an example, the shift parameter hasdifferent values for the chroma component and the luma component. Inanother example, the initial weight values for the chroma component aresmaller than the initial weight values for the luma component, thus theweights for the chroma components can descend to zero sooner.

According to another aspect of the disclosure, PDPC can be disabled forcertain color components. In an embodiment, the PDPC is enabled for lumacomponent.

In another embodiment, PDPC is disabled for chroma component coded usinga pre-defined set of intra prediction modes. In an example, thepre-defined set of intra prediction modes includes the intra predictionmodes which are adjacent to but not equal to diagonal modes (mode 2 andmode 66 when 65 angular intra prediction modes are used). In anotherexample, the pre-defined set of intra prediction modes includes thediagonal intra prediction modes 2 and 66 when 65 angular intraprediction modes are used.

According to another aspect of the disclosure, the initial values of theweights wT and wL of PDPC, i.e., the values of wT and wL of the top-leftsample in current block, are defined depending on coded information,including but not limited to color component, block sizes, and intraprediction modes. In an embodiment, the initial values of wT and wL ofPDPC are halved for chroma component comparing to the initial values ofwT and wL of PDPC for luma component. In an example, when PDPC isapplied on mode 2 and mode 66 (when 65 angular intra prediction modesare applied), the initial values of wT and wL are 8 for the chromacomponent, and 16 for the luma component.

According to another aspect of the disclosure, when the PDPC process isapplied with restrictions, and when a reference sample is not available,for example, out of a predefined range of reference samples, theassociated weight (wT, wL and wTL) can be set to 0 to avoid off-chipmemory access delay. In an example, the reference samples in thepre-defined range are stored using on-chip memory, and the otherreference samples are stored using off-chip memory.

In an example, the pre-defined range of reference samples includes thetop 2W+K reference samples, and left reference 2H+L samples, where W andH are the width and height of current block, and K and L are pre-definedvalues. Example values of K and L include 1, 2, 3, 4, 5, . . . , 16.

In another example, the pre-defined range of reference samples includesthe same range of reference samples that is used for generating theregular (or non-PDPC) intra prediction block.

FIG. 11 shows a flow chart outlining a process (1100) according to anembodiment of the disclosure. The process (1100) can be used in thereconstruction of a block coded in intra mode, so to generate aprediction block for the block under reconstruction. In variousembodiments, the process (1100) are executed by processing circuitry,such as the processing circuitry in the terminal devices (310), (320),(330) and (340), the processing circuitry that performs functions of thevideo encoder (403), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the video decoder (510), the processing circuitry thatperforms functions of the video encoder (603), and the like. In someembodiments, the process (1100) is implemented in software instructions,thus when the processing circuitry executes the software instructions,the processing circuitry performs the process (1100). The process startsat (S1101) and proceeds to (S1110)

At (S1110), prediction information of the current block is decoded fromthe coded video bitstream. The prediction information is indicative ofan intra prediction mode.

At (S1120), the current block with the intra prediction mode is checkedto determine whether the current block meets a restriction condition,such as a block size condition, that limits an application of a PDPCprocess in the reconstruction of the current block. In some examples,the block size condition limits the application of the PDPC in thereconstructions of the current block when the application of the PDPC inthe reconstructions of the current block uses additional referencesamples other than reference samples used in angular based intraprediction according to the intra prediction mode. In some examples, therestriction condition is based on sizes of the current block toenable/disable the application of the PDPC for the current block. Insome examples, the restriction condition is used to limit a subset ofthe current block for the application of the PDPC process. In someexamples, the restriction condition is applied to specific colorcomponent. In some examples, the weight parameters (e.g., descendingspeed of the weights, the initial values of the weights) for referencesamples are suitably configured to implement the restriction condition.

At (S1130), the application of the PDPC is excluded in a reconstructionof at least one sample of the current block when the restrictioncondition, e.g., the block size condition, is met. Then, the processproceeds to (S1199) and terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 12 shows a computersystem (1200) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 12 for computer system (1200) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1200).

Computer system (1200) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1201), mouse (1202), trackpad (1203), touchscreen (1210), data-glove (not shown), joystick (1205), microphone(1206), scanner (1207), camera (1208).

Computer system (1200) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1210), data-glove (not shown), or joystick (1205), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1209), headphones(not depicted)), visual output devices (such as screens (1210) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1200) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1220) with CD/DVD or the like media (1221), thumb-drive (1222),removable hard drive or solid state drive (1223), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1200) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1249) (such as, for example USB ports of thecomputer system (1200)); others are commonly integrated into the core ofthe computer system (1200) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1200) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1240) of thecomputer system (1200).

The core (1240) can include one or more Central Processing Units (CPU)(1241), Graphics Processing Units (GPU) (1242), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1243), hardware accelerators for certain tasks (1244), and so forth.These devices, along with Read-only memory (ROM) (1245), Random-accessmemory (1246), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1247), may be connectedthrough a system bus (1248). In some computer systems, the system bus(1248) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1248),or through a peripheral bus (1249). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1241), GPUs (1242), FPGAs (1243), and accelerators (1244) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1245) or RAM (1246). Transitional data can be also be stored in RAM(1246), whereas permanent data can be stored for example, in theinternal mass storage (1247). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1241), GPU (1242), massstorage (1247), ROM (1245), RAM (1246), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1200), and specifically the core (1240) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1240) that are of non-transitorynature, such as core-internal mass storage (1247) or ROM (1245). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1240). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1240) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1246) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1244)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

-   JEM: joint exploration model-   VVC: versatile video coding-   BMS: benchmark set-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: decoding prediction information of a current block from acoded video bitstream, the prediction information being indicative of anintra prediction mode; determining whether the current block meets ablock size condition that limits an application of a position dependentintra prediction combination (PDPC) in reconstructions of the currentblock based on sizes of the current block; and excluding the applicationof the PDPC in a reconstruction of at least one sample of the currentblock based on the intra prediction mode when the block size conditionis met.
 2. The method of claim 1, wherein the block size conditionlimits the application of the PDPC in the reconstructions of the currentblock when the application of the PDPC in the reconstructions of thecurrent block uses additional reference samples other than referencesamples used in angular based intra prediction according to the intraprediction mode.
 3. The method of claim 1, further comprising:determining whether one of a width and a height of the current block isequal to two; and disabling the application of the PDPC in thereconstruction of the current block when one of the weight and theheight of the current block is equal to two.
 4. The method of claim 1,further comprising: determining whether the current block is larger thana size threshold; and disabling the application of the PDPC in thereconstruction of the current block when the current block is largerthan the size threshold.
 5. The method of claim 1, further comprising:determining whether a ratio of two sides of the current block meets anarrow shape condition; and disabling the application of the PDPC in thereconstruction of the current block when the ratio meets the narrowshape condition.
 6. The method of claim 1, further comprising: selectinga subset of samples in the current block for the application of thePDPC; reconstructing the subset of samples with the application of thePDPC; and reconstructing at least one other sample in the current blockwithout the application of the PDPC.
 7. The method of claim 6, furthercomprising: selecting one or more left columns in the current block forthe application of the PDPC when the current block has more columns thanrows and the intra prediction mode is a diagonal mode; and selecting oneor more top rows in the current block for the application of the PDPCwhen the current block has more rows than columns and the intraprediction mode is a diagonal mode.
 8. The method of claim 6, furthercomprising: increasing a descending speed of a weight for weightingreference samples, the weight descending along a side of the currentblock according to the descending speed.
 9. The method of claim 6,further comprising: reducing an initial value of a weight for weightingreference samples, the weight descending along a side of the currentblock from the initial value.
 10. The method of claim 6, furthercomprising: setting a first descending speed for weighting in the PDPCfor a chroma component to be larger than a second descending speed forweighting in the PDPC for a luma component.
 11. The method of claim 1,further comprising: disabling the application of the PDPC in thereconstruction of chroma samples.
 12. The method of claim 11, furthercomprising: disabling the application of the PDPC in the reconstructionof chroma samples when the intra prediction mode is one in a predefinedset of intra prediction modes.
 13. The method of claim 1, furthercomprising: determining initial values for weights that descend alongsides of the current block based on at least one of a color index, sizesof the current block and the intra prediction mode.
 14. The method ofclaim 1, further comprising: determining whether a reference sample inthe application of the PDPC is out of a predefined range; and setting aweight for the reference sample to be zero when the reference sample isout of the predefined range.
 15. An apparatus for video decoding,comprising: processing circuitry configured to: decode predictioninformation of a current block from a coded video bitstream, theprediction information being indicative of an intra prediction mode;determine whether the current block meets a block size condition thatlimits an application of a position dependent intra predictioncombination (PDPC) in reconstructions of the current block based onsizes of the current block; and exclude the application of the PDPC in areconstruction of at least one sample of the current block based on theintra prediction mode when the block size condition is met.
 16. Theapparatus of claim 15, wherein the block size condition limits theapplication of the PDPC in the reconstructions of the current block whenthe application of the PDPC in the reconstructions of the current blockuses additional reference samples other than reference samples used inangular based intra prediction according to the intra prediction mode.17. The apparatus of claim 15, wherein the processing circuitry isfurther configured to: determine whether one of a width and a height ofthe current block is equal to two; and disable the application of thePDPC in the reconstruction of the current block when one of the weightand the height of the current block is equal to two.
 18. The apparatusof claim 15, wherein the processing circuitry is further configured to:determine whether the current block is larger than a size threshold; anddisable the application of the PDPC in the reconstruction of the currentblock when the current block is larger than the size threshold.
 19. Theapparatus of claim 15, wherein the processing circuitry is furtherconfigured to: determine whether a ratio of two sides of the currentblock meets a narrow shape condition; and disable the application of thePDPC in the reconstruction of the current block when the ratio meets thenarrow shape condition.
 20. The apparatus of claim 15, wherein when theblock size condition is met, the processing circuitry is furtherconfigured to: select a subset of samples in the current block for theapplication of the PDPC; reconstruct the subset of samples with theapplication of the PDPC; and reconstruct at least one other sample inthe current block without the application of the PDPC.